Indoor positioning systems (IPS) enable the location of an object to be identified within an indoor location. In some cases, the object may determine its location in relation to reference points, and in other cases, systems external to the object determine the location of the object.
There exist a wide range of technologies for IPS, including physical sensing, magnetic sensing, and use of audio waves or electro-magnetic waves (including technologies using human-visible light and technologies using non-human-visible light). IPS technologies may also be classified according to whether the positioning system is ‘active’, ‘passive’, or ‘active passive’.
In an ‘active’ system, one or more elements of the system send out reference signals which are received by one or more other elements of the system. For example, one type of active system has Bluetooth beacons which send out reference signals that are detected by nearby smartphones.
An active-passive system (or a ‘reflective’ system) has one element of the system which emits a reference signal that may be reflected by other elements of the system (in a passive manner) or by elements of the indoor environment. An exemplary active-passive system is a system that uses acoustic range-finding to measure the time of flight of an emitted acoustic wave that bounces off (echoes from) solid objects of the indoor environment.
Another system uses human-visible light waves for indoor positioning. Such systems invariably use a form of Visible Light Communication (VLC) to convey details that allow an electronic receiver to determine its own location. In such systems, light fixtures may be modified such that the visible light they emit contains a modulation of additional information such as the light's physical coordinates or a serial number. The modulation is typically sufficiently rapid so as not to be noticeable by the human eye. More advanced systems allow the approximate location of the receiver within the room to be determined by measuring the relative intensity of the modulated light beams from multiple fixtures.
Similarly, in active technologies using non-human visible light such as infra-red, there is a modulation of the light source to allow positional information to be determined. One particularly successful such coding scheme, as implemented in the “Lighthouse” system of the HTC Vive, involves the high-speed sweeping of fans of infra-red light across a room, thus providing an encoding of beam position as a function of time. This allows a receiving device to determine its position by considering the time of arrival of such beams relative to a reference pulse of light.
Some passive technologies utilize human-visible light and non-human-visible light. Such technologies are generally constructed around the principles of using some form of camera to capture images of the device's surroundings and of extrapolating the camera's position from those images, and from past calibrations. Multiple cameras may be used to give additional images and allow triangulation. High-resolution cameras (such as 8 megapixel) may be used to improve accuracy. The computational requirements for performing such extrapolations are significant, and heavily impact the cost, power, and accuracy of such systems.
Without camera and computation, a passive system using light may be limited to basic measurements, such as estimating the distance the receiver has travelled down a corridor by detecting proximity to ceiling lights by measuring overall light level, and counting the number light level fluctuations that had been experienced.
PIR (Passive Infra-Red) detectors have sensors with two cells, and focus infra-red light waves from different areas of the ‘scene’ onto cells alternatively, in order to detect movement of warm objects in the scene.
Beacon-based systems (i.e. systems which install beacons to provide a pre-defined light source) offer the best performance, but the installation of beacons is a key disincentive to user adoption in terms of inconvenience and cost.
The following documents discuss various systems to measure positions of optical targets: U.S. Pat. No. 6,324,296, U.S. Pat. No. 4,973,156 and US 2003/0083844.